微量活性组元氧对焊接熔池Marangoni对流和熔池形貌影响的数值模拟

针对SUS304不锈钢的定点钨极惰性气体保护焊过程,建立三维瞬态定点热源作用下的焊接熔池数学模型,系统研究了不同氧含量下的熔池温度场、速度场以及熔池形貌演变过程.结果表明:随着熔池中活性组元氧的增加,熔池内的对流模式经历了以外对流为主、内外对流共存到以内对流为主的演变过程,熔池形貌由浅且宽形、"勺"形变成深且窄形.熔池中微量氧直接影响熔池表面张力温度梯度系数,改变熔池表面Marangoni对流模式和熔池最终形貌.当氧含量低于80×10-6时,熔池表面以外向Marangoni对流为主,熔池形貌宽且浅;当氧含量超过120×10-6时,熔池表面以内向Marangoni对流为主,熔池形貌窄且深;当氧含量处于(80-120)×10-6之间时,熔池形貌为"勺"形,并且随时间的增加,熔池内外对流区域逐渐变小,内对流区域逐渐变大.定点联合保护焊实验结果表明,熔池形貌变化规律的模拟结果与实验结果吻合.

Numerical simulation of effects of the minor active-element oxygen on the Marangoni convection and the weld shape

A mathematical model was developed to calculate the 3D transient temperature, velocity distribution and the evolution of weld pool shapes in a stationary gas tungsten arc (GTA) weld pool on 304 stainless steels with different oxygen content. The results indicate that when the oxygen content increases, the convection pattern in the weld pool undergoes a dominant outward convection, outward on pool center together with inward on pool periphery, and a dominant inward convection. Accordingly, the weld pool evolves from a shallow wide shape, a spoon-like shape to a deep narrow one. The minor active-element oxygen in the weld pool influences on the temperature coefficient of the surface tension, directly, which leads to the significant change of the Marangoni convection pattern and hence the weld shape. When the oxygen content is below 80ppm, an outward Marangoni convection pattern on the weld pool surface occurs, and forms a shallow and wide weld shape. As the oxygen content exceeding 120ppm, the Marangoni convection changes to inward direction and the weld shape varies from a shallow and wide shape to a deep and narrow one. When the oxygen content is between 80ppm and 120ppm, the weld pool exhibits a spoon-like shape. And as time going, the outward convection region in the weld pool becomes smaller gradually, and the inward convection region becomes larger. The simulation results agree well with the experimental data under Ar-O2 mixed shielding stationary GTA welding on SUS304 plates.